1. Field of the Invention
The present invention relates to an ultrasound endoscope configured so that an ultrasound transducer unit is attachable to and detachable from a distal end portion of an insertion portion configured to be inserted into a subject.
2. Description of the Related Art
An ultrasound endoscope is well known which obtains an ultrasound image of an examination target region by transmitting ultrasound to the examination target region in a subject from an ultrasound transducer held in a housing of an ultrasound transducer unit provided on a distal end portion of an insertion portion and receiving the ultrasound from the examination target region.
Further, a configuration is well known in which the ultrasound transducer unit is attachable to and detachable from the distal end portion of the insertion portion. More specifically, a configuration is well known in which, by a proximal end side of the housing of the ultrasound transducer unit being freely fitted into an ultrasound transducer unit mounting hole (hereinafter referred to simply as a mounting hole) found in a distal end portion body constituting the distal end portion, and screws being freely screwed into screw holes formed in outer circumferences of the distal end portion body and the housing, from an outer side of the distal end portion in a diameter direction, the housing is attachable to and detachable from the mounting hole.
Here, there is a problem that, if countersunk screws having head portions are used as the screws for fixing the housing to the distal end portion body, the head portions project from an outer circumferential face of the distal end portion body after the screws are screwed in the respective screw holes, and reduction of a diameter of the distal end portion of the outer circumferential face is hindered.
In view of such a problem, Japanese Patent Application Laid-Open Publication No. 2002-143166 discloses a configuration of an ultrasound endoscope in which the head portions of the screws are prevented from projecting from the outer circumferential face of the distal end portion body by adopting counterbore holes as the screw holes in which the screws are screwed on the distal end portion body.
By the way, as disclosed in Japanese Patent Application Laid-Open Publication No. 2002-143166, when the housing is screwedly fixed relative to the mounting hole of the distal end portion body, a distal end side of the housing which has the ultrasound transducer inside projects forward more than a distal end face of the distal end portion body. Note that the housing is positioned by a proximal end of the housing being caused to come into contact with a part of the distal end portion body.
Therefore, if a diameter-increased part which protrudes outside in the diameter direction exists on an outer circumferential face on the distal end side of the housing, a circumferential gap occurs along a circumferential direction of the distal end portion, between the diameter-increased part and the distal end face of the distal end portion body due to design tolerance.
Here, the insertion portion is a part configured to be inserted into a subject as described above. Therefore, if a gap occurs on an outer surface, dirt accumulates in the gap.
When dirt accumulates, hygiene problems occur. Therefore, an operator has to remove the dirt in the gap each time he uses the endoscope, and it is very troublesome to the operator. Therefore, a configuration is well known in which the circumferential gap which has occurred on the outer surface is filled with adhesive or the like.